1. Field of the Invention
The invention relates to a method and apparatus for manufacturing high quality crystals, particularly monocrystals, which are useful in the production of electrical and/or electro-optical components.
2. Prior Art
Extremely high standards are required of monocrystals which are utilized as the starting materials for electronic and/or electro-optical components relative to their purity, homogeneity and crystal quality. Therefore, in the manufacture of such crystals, particular attention must be directed toward the stability of the position and/or shape of the solid-liquid interphase. In addition, heterogeneous nucleation must be avoided. In order to attain stable solid-liquid interphases and avoid heterogeneous nucleation, it is necessary to establish defined material and thermal energy flows, which are adjustable by gradients of temperature and composition. As a consequence of such gradients, density gradients occur in the growth media of a crystal, i.e., a melt, which due to gravitational forces can produce convection currents in the liquid/gaseous phase. Such convection currents can be stationary (laminar) or non-stationary (oscillating or turbulent). Analagous crystal growth conditions occur whether the crystal is grown from a melt or from a gas phase.
During crystal growth, stationary convection currents have a positive effect in that they stabilize the growth speed as well as the macroscopic form of the growth interphase (i.e., phase boundary). Further, such stationary convection currents increase the material transport, which is extremely significant in terms of dopant distribution and speed of crystal growth, whether from liquids or gas phases. Non-stationary convection currents, by way of contrast, always produce a time-varying variation in the growth speed as well as in the thickness of a diffusion boundary layer. This inevitably causes a non-homogeneous crystal growth.